This invention relates to improved systems for applying liquid coatings to sheet products, particularly with the use of a transfer roll intermediate a coating reservoir and the sheet to be coated.
A substantial amount of attention has been given to improving coating processes over recent years. Whether for improvements in greater coating uniformity, in thinner coatings, or in achieving more severe processing conditions, there has been an increased amount of interest in this area of art. For example U.S. Pat. No. 4,387,124 describes a coating apparatus using a geometrical flow-divider to aid the distribution of a non-Newtonian fluid onto a web while a resilient seal means was used to maintain a small amount of liquid coating close to the web being coated: U.S. Pat. No. 3,533,833 also discloses a somewhat similar apparatus wherein a coating is applied directly to a web from a reservoir.
Neither of the above-described coating systems take advantage of a transfer-roll metering member and each utilize rather difficult-to-clean apparatus.
In many applications use of a transfer roll is desirable. Nevertheless, there have been serious drawbacks to using such a roll when the coating is to be very thin and when the roll is to be used at high speed. For example, there has been, in addition to the problem of maintaining excellent uniformity of the coating carried by the transfer roll, the problem of avoiding premature drying of the coating on the roll. All of this must be accomplished while metering a uniformlymixed coating fluid across on economically-suitable width of web to be coated.
It is the solution of such problems and allied problems that work leading to the present invention was undertaken.